1. Field of the Invention
The invention relates to stain resistant and soil resistant polyamide compositions and fibers formed therefrom, the fibers being particularly useful in the manufacture of textile articles, carpets and floorcoverings.
2. The Prior Art
Carpet yarns prepared from polyamide fibers are subject to staining by a variety of foods, drinks and many other compositions with which it comes in accidental contact. The uptake of acid dye stains from, for example, soft drinks, is a particularly vexing problem for polyamide fibers due to the availability therein of acid dye sites such as amine end groups and amide linkages. Several methods have been suggested for enhancing the resistance of polyamide fibers to acid dye stains. One approach is to apply a so-called topical "stain blocker" coating to the surfaces of the polyamide fibers to prevent access to the acid dye sites therein by the acid dye staining composition. One of the main types of topical stainblocker are sulfonated aromatic condensates (SAC). There are a number of patents covering SACs. Examples of the method include U.S. Pat. Nos. 5,145,486, 4,680,212 and 4,780,099. Polyamides that are topically coated with SACs have the disadvantage that the topical coating is removed during use and maintenance. Gradual removal of the coating will also occur during cleaning with water and detergents. Fibers used for carpet applications may be regularly cleaned with alkaline-based cleaning agents. SAC topical coatings are easily removed using these types of cleaning agents. The topical coating will also be gradually removed during normal wear of the fiber. In addition to their removal during use and maintenance, SACs generally have inferior resistance to light, oxides of nitrogen, and bleach, the latter being commonly used for the cleaning of industrial textiles and carpets. Also, the base color of SACs is not colorless and thus may change the shade of the color of the yarn.
Another approach for enhancing the resistance of polyamide fibers to acid dye stains is to form the fibers from polyamides prepared by copolymerizing monomers, some of which contain sulfonate moieties. Typical of such systems are those disclosed in U.S. Pat. Nos. 3,542,743, 3,846,507, 3,898,200, 4,391,968, 5,108,684, and 5,164,261 and EP 517,203. All of these prior art patents teach that aryl sulfonate units, when added at the start of the polymerization with the other desired monomers, act as comonomers and become integral parts of the polyamide chain. All of these patents are concerned with modifying the dyeing or stain resistant characteristics of the polyamide.
Fibers are generally prepared from polyamides by melt spinning. Sulfonate-containing polyamides generally have higher melt viscosities than non-sulfonate-containing polyamides for equivalent relative solution viscosities, which limits the extent of polymerization that can practically be achieved in batch autoclave reaction vessels due to the retardation thereby of the rate of polymerization, as well as hinderance of effective discharge of the polymerized melt from the reactor. In addition, the presence of sulfonates which have surfactant properties promotes excessive foaming during the melt polymerization process, resulting in poor agitation of the reaction mixture and non-uniformity of product. An additional disadvantage associated with sulfonate-containing polyamide copolymers is that they are generally more difficult to dry than sulfonate-free polyamides due to the hygroscopic nature of the sulfonate groups.
Yarns having different depths of color require different levels of stain protection. Thus, light shaded colors show the presence of stains more than darker colors. It would be advantageous, therefore, to be able to provide different levels of stain resistance to polyamides depending upon the ultimate yarn color without having to provide a separate polyamide feedstock for optimum formulation of each color yarn.
In addition to the problems of staining of polyamide fibers, soiling of polyamide fibers is also an issue. Fibers used in textile, carpet and flooring applications are desirably low in soil pick-up, i.e., the fiber does not attract soil, and secondly the fiber is easy to clean once it is soiled. Soil proofing of polyamides typically involves one of two approaches. Firstly, a coating may be placed on the fiber which is "sacrificial" in nature, i.e., it is designed to pick up soil, but then must be removed in a cleaning process. Starch is a well known and long practiced example. Such an approach has the drawback that the fiber needs to be recoated after each cleaning to maintain its soil resistance. The second approach to soil proofing is the use of a different type of coating to change the surface energy or hydrophilic/hydrophobic balance of the polyamide, thus making it less attractive to soil. Fluorinated compounds are the most favored species in this area, applied as a topical coating to the fiber. The fluorochemical compounds are coated onto the fiber to prevent or reduce the wetting of the surface by minimizing the contact between the fiber surface and substances that can soil the fiber, making the substance easier to remove. Examples of patents in this area include U.S. Pat. Nos. 3,816,167, 3,896,035, RE30,337 and 4,043,964. The use of topical coatings of the latter type have the similar disadvantages to SACs in that they are removed from the carpet during use, routine maintenance and cleaning.
It is an object of the present invention to provide a novel and highly advantageous approach for imparting stain resistance to fibers formed from polyamides. It is yet another object of the present invention to provide stain resistant polyamide fibers with improved soil resistance in that they have low affinity for soil attraction, and if soiled, are then easy to clean.